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  <script>
    var num1 = 10;
    var num2 = 20;
    var sign = "+";
    function count(a,b,s){
      var result = 0;
      switch(s){
        case "+":result = a + b;break;
        case "-":result = a - b;break;
        case "*":result = a * b;break;
        case "/":result = a / b;break;
      }
      return result;
    }
    console.log(count(num1,num2,sign));
  </script>
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